1. Field of the Invention
The present invention relates to a cartridge case including a tape reel with a hub in the shape of a bottomed cylinder and a locking member that prevents rotation of the tape reel, and to an information recording medium equipped with the cartridge case.
2. Description of the Related Art
In Japanese Laid-Open Patent Publication No. 2002-100148, the present applicant has disclosed a single reel-type tape cartridge as one example of this type of information recording medium. This tape cartridge is constructed by enclosing a single tape reel inside a main case so that the tape reel is rotatable. The tape reel, around which a tape is wound, has a hub in the shape of a bottomed cylinder, with engaging teeth being formed on an inner surface of the base plate of the hub. A brake lock that is energized by a brake spring and restricts rotation of the tape reel is also enclosed inside the main case. The brake lock is constructed so that teeth that engage the engaging teeth of the hub are formed on the lower surface of the brake lock and a guided protrusion that engages a positioning part provided on the inner surface of the upper case that constructs the main case is formed on an upper part of the brake lock. Here, as shown in FIG. 15, the positioning part of the main case (the upper case) is composed of four column-like guide protrusions 101. Also, as shown in FIG. 16, the guided protrusion of the brake lock is constructed so as to be shaped like a cross when viewed from above, with four guide channels 102 that are oblong when viewed from above and engage the respective guide protrusions 101 being formed in the shape of a cross. When this tape cartridge is not in use, as shown in FIG. 17, the brake lock is moved toward the base plate of the hub while being guided in a state where the guide protrusions 101 that respectively engage the guide channels 102 restrict rotation of the brake lock, so that the teeth of the brake lock and the engaging teeth of the hub engage one another. Accordingly, the tape reel is locked by the brake lock and the guide protrusions 101 in a state where rotation is prohibited. On the other hand, during use of the tape cartridge, by pressing up the brake lock with a brake releasing plate disposed between the base plate of the hub and the brake lock, the locking is released and rotation of the tape reel becomes possible.
By investigating the tape cartridge described above, the present inventors discovered the following problem to be solved. That is, with the above tape cartridge, by causing the guide protrusions 101 of the main case to engage the respective guide channels 102 of the brake lock, rotation of the brake lock is restricted and the brake lock is guided toward the base plate of the hub. That is, to make it possible for the brake lock to move smoothly, the dimensions of the guide protrusions 101 and the guide channels 102 are set so that a predetermined clearance is maintained between the guide protrusions 101 and the guide channels 102 when in engagement. However, as shown in FIGS. 15 to 17, since the shapes of the guide protrusions 101 and the guide channels 102 are complex, when a plurality of similar molds are used or when a multiple cavity mold is used to injection mold the main case and the brake lock, the dimensions of the guide protrusions 101 and the guide channels 102 fluctuate between individual molds or individual cavities. Accordingly, there can be fluctuations in the respective clearances between the guide protrusions 101 and the guide channels 102.
Also, as shown in FIG. 17, since the tape cartridge uses a construction where the four column-shaped guide protrusions 101 engage the four oblong guide channels 102 when viewed from above, by rotating the brake lock by 90° to change the orientation with respect to the main case when the guide protrusions 101 and the guide channels 102 are brought into engagement, it is possible to have any of the guide protrusions 101 engage any of the guide channels 102. This means that when there are fluctuations in the dimensions of the respective guide protrusions 101 and the respective guide channels 102, the clearances between the guide protrusions 101 and the respective guide channels 102 can fluctuate even more depending on the orientation of the brake lock with respect to the main case when the guide protrusions 101 and the guide channels 102 are brought into engagement. Accordingly, the brake lock can become slightly inclined with respect to the inner surface of the main case (upper case) due to such fluctuations in the clearance. Also, due to its construction, the tape cartridge has a characteristic whereby even if the respective clearances between the guide protrusions 101 and the guide channels 102 are all identical, the brake lock will be slightly more inclined with respect to the inner surface of the main case in directions (for example, the direction shown by the arrow C in FIG. 17) at an angle of 45°, for example, to the lengthwise directions of the guide channels 102 (i.e., the directions shown by the arrows A and B in FIG. 17) than in the lengthwise directions of the guide channels 102. Accordingly, with this tape cartridge, due to this characteristic and the brake lock becoming inclined due to the fluctuations in clearance described above, there is the risk of the hub contacting the brake lock and producing abnormal noise.
Also, due to the fluctuations in the clearance described above, when the tape reel is rotating in a state where the brake releasing plate presses up the brake lock, there are cases when there is misalignment between the central axis of the brake releasing plate that rotates together with the tape reel and the central axis of the brake lock. When such misalignment occurs, the brake lock vibrates due to a force that moves the brake lock toward the outer periphery and a force whereby a brake spring attempts to restore the brake lock to its original position, resulting in the risk of abnormal noise.